Hello

Could you point me to some resources for studying:

Optimal design / specification for lattice-frame booms loaded in pure

compression - as you would find for classic derricks (gin-pole,

stiffleg-derrick, ...).

Can't carry books with me, so favour on-line learning resources.

I have studied trusses before (lattice frame loaded in beam) - for

small foot-bridge. I'm a metallurgist (scientist) and welder.

Already learned engineering concept that for compression members the

compression load limit may (is likely to be) limited by instability

(failure by local bucking) at below the compression yield force given

the cross-sectional area.

Anyone tell me about my conjecture and whether it is overcomplicated

(there's simplifying factors) or incomplete (there's other things to

be considered) or whatever...

My guess is that for a given mass per unit length, starting from a

very slender boom, the wider the spacing in cross-section of the

longitudinal members the higher the load-carrying capability - until

compression instability of the longer straight lengths of the lattice

"triangle sides" dominates and the optimum spacing of the longitudinal

structurals is passed. Then I have no clue what is the optimal size

of tube - for given mass per unit length the tube is stiffer if larger

diameter but if of larger diameter it must have smaller wall thickness

- hence buckling instability would limit how big is beyond optimum.

Then there is plastic design and damage tolerance which might make

smaller thicker tubes attractive for real applications.

Square cross-section (four longitudinal members) or triangular

cross-section (three longitudinal members)?

I'm thinking in the few metres length range. And makeable given a

stack of tube and a MIG, stick or TIG-welding machine

Haven't found anything in Blodgett "Design of welded structures" (US)

or The Steel Construction Institute's "Steel Designers; Manual"

(UK). (?)

If I came by a way of optimal and achievable design I might be able to

do some tests making and compressing some samples over the winter

season.

Richard Smith

- posted 12 years ago